One of the research objectives is to provide direct evidence for the existence of different fibrins, generically termed "cement fibrin", and for fibrinogens ("fibrin-ogens") in submicroscopic dimensions in the proximity of the endothelium. Antibodies to fibrinogen (fibrin), labeled with either ferritin or heme-octapeptide, will be used in an attempt to find out whether the endoendothelial layer and associated structures (diaphragms of fenestrae, plasmalemmal vesicles, basement membrane) contain fibrinogen and/or fibrin. This study will be supplemented with NH2-terminal analysis of the adsorbed proteins. The other objective concerns the polymerization of fibrinogen and its presence at the proposed vascular sites. It was recently found by Blomback et al. that the N-terminal disulfide knot (N-DSK) of fibrinogen is hidden in the molecule. It appears to be unfolded during exposure to thrombin and new antigenic determinants seem to be exposed at the same time. This unfolding may not necessarily be induced by thrombin or CNBr, but also by shearing forces, which are present in proximity to the vessel wall. Radioactively labeled antibodies to N-DSK will be used to test the hypothesis that this antigenic determinant is exposed in the fibrinogen molecule as a result of shearing without partial proteolysis. Rheological measurements of viscous resistance and viscoelasticity of surface layers of fibrinogen will be correlated to the immunochemical and electron microscopic studies. The rheological measurements will also be made of surface layers of plasma proteins other than fibrinogen and of different plasma protein systems containing platelets, red and white blood cells.